1. Field of the Invention
This present invention relates to a centrifugal clutch.
2. Description of the Related Art
As shown in FIG. 5, a centrifugal clutch C basically includes a clutch drum 90, a plurality of clutch shoes 91 that are placed in the clutch drum 90 so as to shift in the radial direction, and allowed to shift outward in the radial direction by centrifugal force to be frictionally engaged with the inner face of the clutch drum 90 (this means the two members are prevented from moving relatively by the friction) and springs 92 that pull the clutch shoes 91 inward in the radial direction in a biased manner to keep the clutch shoes 91 separated from the inner circumferential face of the clutch drum 90 in a normal state. As shown in FIG. 5, a flange plate 93 having a boss 93a that is rotated by a rotary shaft J is placed between the clutch shoes 91 inside the clutch drum 90; thus, pins 93b on the flange plate 93 side and pins 91a on the clutch shoe 91 side are inserted into holes 94b and holes 94a which are formed in both end portions of each of arm members 94 so that the arm members 94 are attached in a manner so as to freely rotate, with the springs 92 being laid between the flange plate 93 and each clutch shoe 91.
In this centrifugal clutch C, when the rotary shaft J has reached a rotational speed exceeding a predetermined level, the clutch shoes 91 are allowed to shift outward in the radial direction against spring force of the springs 92 so that the lining of each clutch shoe 91 is made in contact with the inner circumferential face of the clutch drum 90 and frictionally engaged therewith; thus, the clutch drum 90 is allowed to rotate integrally with the rotary shaft J. In contrast, when the rotational speed of the rotary shaft J becomes lower than the predetermined level, the clutch shoes 91 are shifted inward in the radial direction so that the lining of each clutch shoe 91 is released from the inner circumferential face of the clutch drum 90, with the result that the rotational force of the rotary shaft J is not transmitted to the clutch drum 90.
Other examples of this type of centrifugal clutch have been disclosed in Japanese Utility Model Application Publication Laid-Open No. 1-165339 (1988) and in Japanese Utility Model Application Publication Laid-Open No. 57-28937 (1982), and these have the same functions as the centrifugal clutch having the above-mentioned structure.
However, the centrifugal clutch C shown in FIG. 5 has the following problems:
(1) Because of the structure in which the pins 93b on the flange plate 93 side and the pins 91a on the clutch shoe 91 side are respectively inserted into the holes 94b and holes 94a which are formed in both end portions of each of the arm members 94 so as to allow the arm members 94 to freely rock, before the lining of the clutch shoe 91 has been frictionally engaged with the inner circumferential face of the clutch drum 90, the front side in the rotation direction of the lining of each clutch shoe 91 collides with the clutch drum 90 (this is indicated by a solid line in FIG. 6) or the rear side in the rotation direction thereof collides with the clutch drum 90 (this is indicated by a two-dot chain line in FIG. 6) to generate continuous big collision noise.
(2) Since the tension and attaching position of each spring 92 are fixed, the lining of the outer face of each clutch shoe 91 wears out to make a gap between the lining and the inner circumferential face of the clutch drum 90 greater than the initial set value, with the result that a delay tends to occur in the timing at which the lining of each clutch shoe 91 is frictionally engaged with the inner circumferential face of the clutch drum 90.